This invention relates to the disposal of toxic waste products. More particularly, it relates to the encapsulation of toxic metals with resinous plastic so that the toxic materials can be properly disposed of.
In U.S. Pat. No. 4,702,862 there is stated in the background of the invention that it is known to mix polyvinylchloride or polyethylene with radioactive waste and pass the mixture through a heated extruder. The mixture is subsequently cast into compact plastic blocks for final storage. This particular patent is an improvement over that process in that radioactive thermoplastic synthetic material is the matrix material. It is also known in the prior art to utilize resinous plastic such as polyethylene to encapsulate a radio active solution in order to form a solid and essentially nonporous, rigid polyethylene body which can be stored either above or below the ground. This is described in U.S. Pat. No. 3,463,738. In U.S. Pat. No. 3,993,579 powdered toxic, high-level radioactive waste is encapsulated in a vitreous carbon which is obtained by carbonizing a resin. The vitreous carbon shapes can be further protected for storage by encasement in a canister with molten aluminum placed around it. Radioactive wastes are also encapsulated in U.S. Pat. No. 4,077,901 wherein a fluid thermosettable resin composition is employed which is of the vinyl ester or unsaturated polyester type. Radioactive wastes are also of concern in U.S. Pat. No. 4,299,721 wherein a container is filled with a predetermined amount of pellets of the radioactive waste and the container then filled with a thermoplastic composition in the molten state. Similarly, U.S. Pat. No. 4,708,822 utilizes pellets of radioactive waste material encapsulated in a cross-linked plastic resin.
It has now been found that an improvement over the prior art processes can be provided especially in the field of disposing of nonradioactive wastes if the toxic materials are encapsulated in a resinous plastic so that a skin of plastic material is provided over the toxic waste material. Neither do the prior art processes teach the use of a two-step process in which the waste materials are first admixed with a resinous plastic and then subsequently processed with additional resinous plastic or with additional molding. This provides the individual waste elements with a coating of resinous plastic as well as the exterior skin. An encapsulated waste product results which is nonporous and inert to all naturally occurring solvents in the environment. An additional factor not considered in the prior art is that the waste material is generally hydroscopic and contains large quantities of water. This causes a boiling of the water in an extruder and in turn irregularities in the surface of the extruded material. The moisture problem is the reason resins and fillers must be completely dry when carrying out current molding processes.
It is an advantage of the present invention to provide a novel encapsulation method for waste materials.
Another advantage is a novel product composed of toxic waste materials which are encapsulated in a plastic matrix such that the materials will not migrate or leach from the matrix.
It is another advantage of this invention to provide a novel method for encapsulating waste materials in a plastic matrix which includes an extruding of the waste material with a plastic resin and subsequent processing steps of regrinding or chopping and subsequent encapsulation.
Another advantage is an encapsulation method wherein the waste products are encapsulated in a body of plastic material which has a film formed over the outside thereof.
Yet another advantage of this invention is a method of the foregoing kind which can be carried out by available molding equipment.
Still another advantage of this invention is a product of the foregoing type which can be formed with indicia marked thereon so as to indicate the potential danger of the encapsulated product.
Other advantages are: an encapsulated product of the foregoing type which because of its size cannot be easily ingested; minimizes exposed surfaces with respect to the volume of the product to reduce potential exposure of the waste product; inhibits UV light absorption for the above described product if stored above the ground; is chemically inert to all naturally occurring substances; permits future reclamation of the waste product and in the event of fracture or cutting, minimizes exposure of the waste material; and affords the encapsulation of liquids.